剑指offer面试题16——数值的整数次方

题目描述

给定一个double类型的浮点数base和int类型的整数exponent。求base的exponent次方。

题目分析

//使用库函数pow()
class Solution {
public:
    double Power(double base, int exponent) {
        double result = pow(base, exponent);
        return result;
    }
};

 

不允许使用库函数的话：

class Solution {
public:
    double Power(double base, int exponent) {
        if(base == 0 && exponent < 0){
            return 0;
        }
        unsigned int absExponent = (unsigned int)(exponent);
        if(exponent < 0)
            absExponent = (unsigned int)(-exponent);
        double result = PowerWithUnsignedExponent(base, absExponent);
        if(exponent < 0)
            result = 1/result;
        return result;
    }
    
    double PowerWithUnsignedExponent(double base, unsigned int exponent){
        if(exponent == 0)
            return 1;
        if(exponent == 1)
            return base;
        double result = PowerWithUnsignedExponent(base, exponent >> 1); //右移 = 除以2
        result *= result;
        if((exponent & 0x1) == 1)  //位与运算符代替求余运算符判断一个数是奇数还是偶数
            result *= base;
        return result;
    }
};